Staged Z-Pinch Experiments on the Mega-Ampere Current Driver Cobra

Previous Staged Z-pinch (SZP 1 experiments at the University of California-Irvine demonstrated that gas liners (or gas-puffs) can efficiently couple energy to a target plasma and implode it uniformly. In those experiments, a 1.5 MA, $1 \mu \mathrm {s}$ current driver was used to implode a magnetized, Kr liner onto a D+ target, producing ~1010 neutrons per shot. Time-of-flight data suggested that primary and secondary neutrons were produced. Recent MHD simulations 2 have suggested that liner composition is important for target shock-heating before the main adiabatic implosion and that pre-magnetization is crucial to achieve uniform implosions.A recent series of experiments were carried out to investigate implosion dynamics using Cornell’s 1 MA, 200 ns current driver COBRA with a goal to help us better understand the SZP physics and benchmark MHD codes. We used an optimized gas injector 3 composed of an annular (1 cm radius) high atomic number (e.g., Ar or Kr) gas-puff and an on-axis plasma gun that delivers the ionized hydrogen target. Liner implosion velocity and stability were studied using laser shadowgraphy and interferometry as well as gated visible and XUV imaging. Target temperature and density were measured with Thomson scattering and X-ray spectroscopy. Experimental data is presented and preliminary analysis is discussed.